spandsp  0.0.6
fsk.h
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1 /*
2  * SpanDSP - a series of DSP components for telephony
3  *
4  * fsk.h - FSK modem transmit and receive parts
5  *
6  * Written by Steve Underwood <steveu@coppice.org>
7  *
8  * Copyright (C) 2003 Steve Underwood
9  *
10  * All rights reserved.
11  *
12  * This program is free software; you can redistribute it and/or modify
13  * it under the terms of the GNU Lesser General Public License version 2.1,
14  * as published by the Free Software Foundation.
15  *
16  * This program is distributed in the hope that it will be useful,
17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19  * GNU Lesser General Public License for more details.
20  *
21  * You should have received a copy of the GNU Lesser General Public
22  * License along with this program; if not, write to the Free Software
23  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
24  */
25 
26 /*! \file */
27 
28 /*! \page fsk_page FSK modems
29 \section fsk_page_sec_1 What does it do?
30 Most of the oldest telephony modems use incoherent FSK modulation. This module can
31 be used to implement both the transmit and receive sides of a number of these
32 modems. There are integrated definitions for:
33 
34  - V.21
35  - V.23
36  - Bell 103
37  - Bell 202
38  - Weitbrecht (Used for TDD - Telecoms Device for the Deaf)
39 
40 The audio output or input is a stream of 16 bit samples, at 8000 samples/second.
41 The transmit and receive sides can be used independantly.
42 
43 \section fsk_page_sec_2 The transmitter
44 
45 The FSK transmitter uses a DDS generator to synthesise the waveform. This
46 naturally produces phase coherent transitions, as the phase update rate is
47 switched, producing a clean spectrum. The symbols are not generally an integer
48 number of samples long. However, the symbol time for the fastest data rate
49 generally used (1200bps) is more than 7 samples long. The jitter resulting from
50 switching at the nearest sample is, therefore, acceptable. No interpolation is
51 used.
52 
53 \section fsk_page_sec_3 The receiver
54 
55 The FSK receiver uses a quadrature correlation technique to demodulate the
56 signal. Two DDS quadrature oscillators are used. The incoming signal is
57 correlated with the oscillator signals over a period of one symbol. The
58 oscillator giving the highest net correlation from its I and Q outputs is the
59 one that matches the frequency being transmitted during the correlation
60 interval. Because the transmission is totally asynchronous, the demodulation
61 process must run sample by sample to find the symbol transitions. The
62 correlation is performed on a sliding window basis, so the computational load of
63 demodulating sample by sample is not great.
64 
65 Two modes of symbol synchronisation are provided:
66 
67  - In synchronous mode, symbol transitions are smoothed, to track their true
68  position in the prescence of high timing jitter. This provides the most
69  reliable symbol recovery in poor signal to noise conditions. However, it
70  takes a little time to settle, so it not really suitable for data streams
71  which must start up instantaneously (e.g. the TDD systems used by hearing
72  impaired people).
73 
74  - In asynchronous mode each transition is taken at face value, with no temporal
75  smoothing. There is no settling time for this mode, but when the signal to
76  noise ratio is very poor it does not perform as well as the synchronous mode.
77 */
78 
79 #if !defined(_SPANDSP_FSK_H_)
80 #define _SPANDSP_FSK_H_
81 
82 /*!
83  FSK modem specification. This defines the frequencies, signal levels and
84  baud rate (== bit rate for simple FSK) for a single channel of an FSK modem.
85 */
86 typedef struct
87 {
88  /*! Short text name for the modem. */
89  const char *name;
90  /*! The frequency of the zero bit state, in Hz */
91  int freq_zero;
92  /*! The frequency of the one bit state, in Hz */
93  int freq_one;
94  /*! The transmit power level, in dBm0 */
95  int tx_level;
96  /*! The minimum acceptable receive power level, in dBm0 */
97  int min_level;
98  /*! The bit rate of the modem, in units of 1/100th bps */
99  int baud_rate;
100 } fsk_spec_t;
101 
102 /* Predefined FSK modem channels */
103 enum
104 {
105  FSK_V21CH1 = 0,
106  FSK_V21CH2,
107  FSK_V23CH1,
108  FSK_V23CH2,
109  FSK_BELL103CH1,
110  FSK_BELL103CH2,
111  FSK_BELL202,
112  FSK_WEITBRECHT, /* 45.45 baud version, used for TDD (Telecom Device for the Deaf) */
113  FSK_WEITBRECHT50, /* 50 baud version, used for TDD (Telecom Device for the Deaf) */
114  FSK_V21CH1_110 /* 110 bps version of V.21 channel 1, as used by V.18 */
115 };
116 
117 enum
118 {
119  FSK_FRAME_MODE_ASYNC = 0,
120  FSK_FRAME_MODE_SYNC = 1,
121  FSK_FRAME_MODE_5N1_FRAMES = 7, /* 5 bits of data + start bit + stop bit */
122  FSK_FRAME_MODE_7N1_FRAMES = 9, /* 7 bits of data + start bit + stop bit */
123  FSK_FRAME_MODE_7E1_FRAMES = 10, /* 7 bits of data + even parity + start bit + stop bit */
124  FSK_FRAME_MODE_7E2_FRAMES = 11 /* 7 bits of data + even parity + start bit + 2 stop bits */
125 };
126 
127 SPAN_DECLARE_DATA extern const fsk_spec_t preset_fsk_specs[];
128 
129 /*!
130  FSK modem transmit descriptor. This defines the state of a single working
131  instance of an FSK modem transmitter.
132 */
134 
135 /* The longest window will probably be 106 for 75 baud */
136 #define FSK_MAX_WINDOW_LEN 128
137 
138 /*!
139  FSK modem receive descriptor. This defines the state of a single working
140  instance of an FSK modem receiver.
141 */
143 
144 #if defined(__cplusplus)
145 extern "C"
146 {
147 #endif
148 
149 /*! Initialise an FSK modem transmit context.
150  \brief Initialise an FSK modem transmit context.
151  \param s The modem context.
152  \param spec The specification of the modem tones and rate.
153  \param get_bit The callback routine used to get the data to be transmitted.
154  \param user_data An opaque pointer.
155  \return A pointer to the modem context, or NULL if there was a problem. */
156 SPAN_DECLARE(fsk_tx_state_t *) fsk_tx_init(fsk_tx_state_t *s,
157  const fsk_spec_t *spec,
158  get_bit_func_t get_bit,
159  void *user_data);
160 
161 SPAN_DECLARE(int) fsk_tx_restart(fsk_tx_state_t *s, const fsk_spec_t *spec);
162 
163 SPAN_DECLARE(int) fsk_tx_release(fsk_tx_state_t *s);
164 
165 SPAN_DECLARE(int) fsk_tx_free(fsk_tx_state_t *s);
166 
167 /*! Adjust an FSK modem transmit context's power output.
168  \brief Adjust an FSK modem transmit context's power output.
169  \param s The modem context.
170  \param power The power level, in dBm0 */
171 SPAN_DECLARE(void) fsk_tx_power(fsk_tx_state_t *s, float power);
172 
173 SPAN_DECLARE(void) fsk_tx_set_get_bit(fsk_tx_state_t *s, get_bit_func_t get_bit, void *user_data);
174 
175 /*! Change the modem status report function associated with an FSK modem transmit context.
176  \brief Change the modem status report function associated with an FSK modem transmit context.
177  \param s The modem context.
178  \param handler The callback routine used to report modem status changes.
179  \param user_data An opaque pointer. */
180 SPAN_DECLARE(void) fsk_tx_set_modem_status_handler(fsk_tx_state_t *s, modem_status_func_t handler, void *user_data);
181 
182 /*! Generate a block of FSK modem audio samples.
183  \brief Generate a block of FSK modem audio samples.
184  \param s The modem context.
185  \param amp The audio sample buffer.
186  \param len The number of samples to be generated.
187  \return The number of samples actually generated.
188 */
189 SPAN_DECLARE_NONSTD(int) fsk_tx(fsk_tx_state_t *s, int16_t amp[], int len);
190 
191 /*! Get the current received signal power.
192  \param s The modem context.
193  \return The signal power, in dBm0. */
194 SPAN_DECLARE(float) fsk_rx_signal_power(fsk_rx_state_t *s);
195 
196 /*! Adjust an FSK modem receive context's carrier detect power threshold.
197  \brief Adjust an FSK modem receive context's carrier detect power threshold.
198  \param s The modem context.
199  \param cutoff The power level, in dBm0 */
200 SPAN_DECLARE(void) fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff);
201 
202 /*! Initialise an FSK modem receive context.
203  \brief Initialise an FSK modem receive context.
204  \param s The modem context.
205  \param spec The specification of the modem tones and rate.
206  \param framing_mode 0 for fully asynchronous mode. 1 for synchronous mode. >1 for
207  this many bits per asynchronous character frame.
208  \param put_bit The callback routine used to put the received data.
209  \param user_data An opaque pointer.
210  \return A pointer to the modem context, or NULL if there was a problem. */
211 SPAN_DECLARE(fsk_rx_state_t *) fsk_rx_init(fsk_rx_state_t *s,
212  const fsk_spec_t *spec,
213  int framing_mode,
215  void *user_data);
216 
217 SPAN_DECLARE(int) fsk_rx_restart(fsk_rx_state_t *s, const fsk_spec_t *spec, int framing_mode);
218 
219 SPAN_DECLARE(int) fsk_rx_release(fsk_rx_state_t *s);
220 
221 SPAN_DECLARE(int) fsk_rx_free(fsk_rx_state_t *s);
222 
223 /*! Process a block of received FSK modem audio samples.
224  \brief Process a block of received FSK modem audio samples.
225  \param s The modem context.
226  \param amp The audio sample buffer.
227  \param len The number of samples in the buffer.
228  \return The number of samples unprocessed.
229 */
230 SPAN_DECLARE_NONSTD(int) fsk_rx(fsk_rx_state_t *s, const int16_t *amp, int len);
231 
232 /*! Fake processing of a missing block of received FSK modem audio samples
233  (e.g due to packet loss).
234  \brief Fake processing of a missing block of received FSK modem audio samples.
235  \param s The modem context.
236  \param len The number of samples to fake.
237  \return The number of samples unprocessed.
238 */
239 SPAN_DECLARE_NONSTD(int) fsk_rx_fillin(fsk_rx_state_t *s, int len);
240 
241 SPAN_DECLARE(void) fsk_rx_set_put_bit(fsk_rx_state_t *s, put_bit_func_t put_bit, void *user_data);
242 
243 /*! Change the modem status report function associated with an FSK modem receive context.
244  \brief Change the modem status report function associated with an FSK modem receive context.
245  \param s The modem context.
246  \param handler The callback routine used to report modem status changes.
247  \param user_data An opaque pointer. */
248 SPAN_DECLARE(void) fsk_rx_set_modem_status_handler(fsk_rx_state_t *s, modem_status_func_t handler, void *user_data);
249 
250 #if defined(__cplusplus)
251 }
252 #endif
253 
254 #endif
255 /*- End of file ------------------------------------------------------------*/
int freq_one
Definition: fsk.h:93
void fsk_tx_power(fsk_tx_state_t *s, float power)
Adjust an FSK modem transmit context&#39;s power output.
Definition: fsk.c:218
int min_level
Definition: fsk.h:97
void fsk_tx_set_modem_status_handler(fsk_tx_state_t *s, modem_status_func_t handler, void *user_data)
Change the modem status report function associated with an FSK modem transmit context.
Definition: fsk.c:231
fsk_rx_state_t * fsk_rx_init(fsk_rx_state_t *s, const fsk_spec_t *spec, int framing_mode, put_bit_func_t put_bit, void *user_data)
Initialise an FSK modem receive context.
Definition: fsk.c:314
int framing_mode
Synchronous/asynchronous framing control.
Definition: private/fsk.h:62
Definition: private/fsk.h:58
Definition: private/fsk.h:33
void(* put_bit_func_t)(void *user_data, int bit)
Definition: async.h:105
int baud_rate
Definition: fsk.h:99
void(* modem_status_func_t)(void *user_data, int status)
Definition: async.h:114
int(* get_bit_func_t)(void *user_data)
Definition: async.h:108
SPAN_DECLARE_NONSTD(int) fsk_tx(fsk_tx_state_t *s
Generate a block of FSK modem audio samples.
const char * name
Definition: fsk.h:89
int tx_level
Definition: fsk.h:95
void fsk_rx_set_modem_status_handler(fsk_rx_state_t *s, modem_status_func_t handler, void *user_data)
Change the modem status report function associated with an FSK modem receive context.
Definition: fsk.c:259
Definition: fsk.h:86
float fsk_rx_signal_power(fsk_rx_state_t *s)
Definition: fsk.c:246
put_bit_func_t put_bit
The callback function used to put each bit received.
Definition: private/fsk.h:64
void fsk_rx_signal_cutoff(fsk_rx_state_t *s, float cutoff)
Adjust an FSK modem receive context&#39;s carrier detect power threshold.
Definition: fsk.c:238
int freq_zero
Definition: fsk.h:91
fsk_tx_state_t * fsk_tx_init(fsk_tx_state_t *s, const fsk_spec_t *spec, get_bit_func_t get_bit, void *user_data)
Initialise an FSK modem transmit context.
Definition: fsk.c:153